Microwave-assisted Michael reactions of 3-(2′-nitrovinyl)indole with indoles on TLC-grade silica gel. A new, facile synthesis of 2,2-bis(3′-indolyl)nitroethanes

3-(2′-Nitrovinyl)indole reacted with indole and 1- and 2-alkylindoles on TLC-grade silica gel under microwave irradiation to furnish in 7–10 min bis(indolyl)nitroethanes in high yields (70–86%). The same products were also obtained in 69–84% yields without microwave irradiation, but the reactions required 8–14 h for completion. Skatole was inert under both sets of conditions.